This blog is about how we can make large space construction by the way of direct polymerisation composite materials in free space environment (Earth orbit, on Moon surface, on asteroids and in far space).

Thursday, 17 May 2012

The temperature in space is tricky. Usual imagination, what
we have on Earth, does not work there. Imagine: there are no walls, furniture,
ground, neighbours, friends and wind (air) surrounded your body. Temperature
depends on the irradiation from the Sun and on internal sources. All bodies
irradiate following Stefan–Boltzmann law.

If no irradiations from neighbours,
your temperature goes to absolute zero, well, not zero, because of space irradiations.
But anyway, it comes to very low temperature; the space flight measurements
give temperatures about -150 C. If you are irradiated by the Sun, your sun-side
will be heated up in dependence on reflectivity of your surface,
thermocapacity, thermoconductivity and geometry of your body. Very quickly you
start to feel, that one side of you is burning (can be +150 C and more), while
the other side is still frozen. You will want to turn. If you turn quickly
enough, your temperature will be more or less steady. So, the rotation of the
body is very important.

Now let’s remember, how the chemical reaction
depends on temperature. At first approximation, the rate of reaction follows Arrhenius
law: the rate increases with temperature. Usually, the curing system is
selected to be non-reacting at storage temperatures so, that uncured material
can be kept in container at transportation without the reaction. Therefore, the
temperature at curing should be higher than on Earth and at transportation.

There are some ways to get it. First of all, rotation of the
construction side by side to the Sun should be so, that each part of the
construction will be heated enough to be cured completely. It does not need
massive efforts, because no friction there, and if the construction is
accelerated it will rotate forever. You have to be smart enough to calculate
the rotation speed and direction. It can be calculated, measured, compared with
experiments on orbit. The regime of rotation can be optimised to get complete
curing in all sides and parts of the construction.

But what can you do on the Moon or on an asteroid? You
cannot rotate the Moon of asteroid as we want. If you are settled down on
equator of the Moon, you can expect heating enough with the turning of the
Moon. But if your construction has to be placed on polar, what is more likely
because of found water there, there is no way to get a heat enough. You have to
heat it with internal sources, for example, with internal electrical heaters.
And you have to be ready to spend a lot of energy during curing reaction. It is
not a huge amount of energy: ISS astronauts spend a comparable amount of energy
to support life there. The construction can be heated partially: sector by
sector, that can decrease an amount of power, you have to apply.

Another way is to use photocuring reaction. There are
compositions that can be cured under UV light. That’s nice way if you need to
cure quickly, on command after storing long time in the container. In such
case, the curing reaction is not so sensitive to the storage temperature, while
the rate of curing anyway depends on temperature. Such photocuring systems can
be suitable for repairmen set. But the photocured materials have usually lower
mechanical strength, lower radiation stability, shorter life-time and narrower
diapason of exploitation conditions, than thermocured materials. These two
kinds of materials (photocured and thermocured) are specialised for different
constructions. You can choose one of them for particular construction and
exploitation conditions.

However, there is a serious problem with the temperature in
space: thermostresses. This problem needs attention. Usually, on Earth the
prepreg (uncured material) is placed into curing oven, heated slowly with
optimised rate of the temperature increase, cured at uniformly distributed
temperature, and cooled slowly. The heating/cooling process is optimised to
avoid the thermostresses in the construction. In space, when the construction
is irradiated from one side, the Sun irradiation creates a temperature
gradient. The curing reaction follows to the temperature gradient in the
construction. Therefore, the different parts of the construction will be cured
at different temperature and will keep memory of the temperature gradient. When
the cured construction changes an orientation, the temperature gradient changes
and it generates the stresses. As higher temperature gradient is at curing, as
higher stresses appear. The stresses deform your construction and decrease the
mechanical strength of the construction.

Because no one large curing oven with temperature
stabilisation is installed in Earth orbit, where you can put your construction
for precise curing, the temperature regime of the construction should be
precisely calculated and the flight regime should be optimised to get
completely cured material of the construction without significant stresses.

All materials, including
polymers, degrade in space environment under high energy cosmic rays, Sun wind,
atomic oxygen of residual Earth atmosphere (if Low Earth Orbit). Since first
space flights, engineers worry about degradation of the materials used for
space ships, satellites, stations. A number of experiments have been done,
when different kinds of materials were exposed on Low Earth Orbits. Then the
materials were delivered on Earth, to laboratories for an investigation. The
structure changes in all polymer materials have been observed, described,
calculated and simulated in laboratory experiments.

First of all, this is an effect
of etching. The materials disappear with time: layer-by-layer. You can find a rate of etching in literature for different kinds of materials. There are
handbooks, database, standards and recommendations how to choose a right
material based on mission, orientation, lifetime and functionality of materials
in particular space construction.

At second, the materials become
brittle, cracked, and finally broken under space conditions. The molecular
structure changes significantly: polymers become crosslinked, depolymerised and
oxidised in dependence of kind of polymer. All these effects in polymers can be
observed in laboratory under plasma and high energy particles. The chemistry of
these processes is based on generation of free radicals, when a high energy
particle hits a macromolecule and forms free radicals. The free radicals are
very active and start to react with neighbour macromolecules. These chemical
reactions transform the initial macromolecules dramatically.

The same radiation effects are observed in macromolecules when uncured polymer with liquid matrix is exposed in UV light, g-irradiation,
X-ray beam, plasma and ion beam.

At first, the etching rate is higher. The uncured polymer degrades quicker than the hard polymer. We measured it. But the difference is only 2 times. Is it significant? Yes, for first two-three hours. But then the polymer becomes hard and stays 15-20 years. Therefore, the contribution of high etching rate, when the polymer was liquid, is neglectable in comparison of low etching rate at the rest of life.

At second, the radiation damaging of the macromolecules is the same. The generated free radicals in matrix can
cause two kinds of reactions: crosslinking and depolymerisation. If right
composition is selected, the crosslinking reactions proceed and the polymer
matrix becomes hard. The same effect as in curing reaction, but without any
hardener! Therefore, the free space environment can play a role of additional
initiator of the crosslinking reaction.

"The space makes polymer hard", as the
journalist wrote about our investigations. That’s true, in the case of uncured
composite the enemy space environment helps us to get durable material. Let’s
use this help smartly.

Tuesday, 8 May 2012

Well, let’s consider the problems of polymerisation in
space: first of all is vacuum.

Low pressure of free space environment is a problem for all
materials, constructions and human during a space flight. This is unusual in
comparison what we have on the “bottom” of our air “ocean”.

At first, the residual gases can inflate the shell of the
construction shortly after launch, when the container with folded shell is
lifted to space. The inflation pressure is very low, if outer pressure becomes
neglectable. This was a reason of some failed space flight missions when large
shell was inflated in Earth orbit, but the uncontrolled inflation broke the
shell. The inflating pressure is close to vapour pressure of cured (hard)
polymer materials, which always contain some dissolved gases, low molecular
fractions and residual solvents. The presence of residual gases is so
dangerous, that the polymer shell can inflate spontaneously after opening of
the container.

What will be, if a liquid resin with high vapour pressure will
be placed into the hermetic shell? Explosion. This is why most projects on
inflation space construction with uncured material inside are not realized. No
one of material experts in space agencies agrees to sign permission, that the
shell with liquid resin inside will be deployed under control.

Can we manage it? Yes, we can.

The prepreg with liquid resin should be placed on external
side of the inflating shell. In such case, the evaporation of liquid resin will
be into space. The inflation process of the shell remains dangerous due to
shell vapour pressure, but with special ventilation we can decrease the
pressure caused by evaporation of low molecular components from the shell
material. And the high vapour pressure of the uncured resin will be not important
for the inflation.

You can ask me:

- wait a minute, it means, that the uncured liquid resin
will be placed directly into space?

- Yes!

- But the resin components will evaporate and disappear with
time. Nothing will remain for curing!

- Yes, if a composition of the resin is wrong. Some people
from ESA tried it, failed and said: “curing in vacuum is impossible”. However,
if the composition is right, the evaporation of components is not a problem.

How can we select a right composition?

Look, if you put a glass of water in vacuum chamber and pump
it, after some time you will see, the water evaporated completely. If you put a
glass of ethylene diamine (the hardener for epoxy resin) into vacuum chamber
and pump it, the ethylene diamine will evaporate too. However, if you look at
the door of vacuum chamber, you can see a rubber O-ring. It is used for hermetisation
of the vacuum chamber door to prevent air coming. This O-rig does not disappear
after long pumping at extremely low pressure and temperature. You see, there
are soft substances that can survive in vacuum. Actually, all materials
evaporate in vacuum including metals, the question is: how fast? We must select
substances suitable for the curing (active) and survival in low pressure (slow
evaporation).

To estimate the dangerous of evaporation, we have to
consider a curing reaction of the polymer matrix together with evaporation. In
literature you can find plenty information about kind of curing reaction, some
of active compositions are certified by space agencies to be used in space for
construction materials. All of these materials consist of minimum two
components: resin and hardener. The reaction of polycondensation is mostly used
for curing of such kind of materials. It means, that the ratio of resin and
hardener is usually optimised to get durable composite after curing. If one
component is lost, the composition remains uncured and the material lost
mechanical characteristics.

Therefore, the right composition should provide low
evaporation rate for both active components: hardener and resin, and the rates
of evaporation should be similar for all active components.

The second problem is cavitation. When uncured liquid
composition contains a lot of low molecular fractions (it does not matter, if
they are active or not) and these fractions evaporate fast, the composition
becomes bubbled in vacuum. These low molecular fractions evaporate too fast and
the vapours are collected into bubbles. If the composition becomes harder with
time, the bubbles cannot move to the surface, stop and form foam. You can see
it, if you buy liquid polyurethane in nearest tool shop and make polyurethane
foam. Similar foam was observed in NASA space experiment during space flight
and they said: “curing in vacuum is impossible”.

Therefore, the right composition should not contain low
molecular fractions which can make bubbles and foam in vacuum.

If the composition does not break the curing reaction and
does not give a foam in vacuum, it can be cured in space. That’s just right
selection based on knowledge of the evaporation rates, composition components,
curing kinetics and some experience. We have found and tested some compositions
up to 10^-5 Pa pressure. They are not expensive and not rare. Some of them in
cured form are certified for space constructions can be used now.

If pressure becomes lower than the vapour pressure of the
components (10-100 Pa for liquid epoxy resins, for example) and the evaporation
has been started, a following decrease of the pressure does not play a role.
For example, if the pressure in Low Earth Orbit is 10^-5-10^-7 Pa (while the
pressure near spaceship depends on sun irradiation, how long is the ship in the
orbit, material of the ship walls and so on and it is usually higher than the
pressure far from the ship), the evaporation will have similar effect on the
curing material as in deep space, when the pressure can be 10^-11 or lower (if
no one has been there and did not put his gases, I mean evaporation).
Therefore, the compositions tested in Earth orbit can be used on Moon, on
asteroids, in Jupiter’s orbit and in another galaxy.

So, a curing of liquid composition in vacuum is not a
problem, while some official referee of my project in Europe said: “that’s
impossible!” and rejected the project.

Wednesday, 2 May 2012

Project:”Large-size antenna dish, shield and frame of space station by the
way of polymerization of composite material on Earth orbit in free space
environment”

The main goal of the project is the development
of the polymerization processes of polymer composite materials in free space
environment and the creation the technology for large-size constructions
on Earth orbit.

The size and mass of modern space
constructions (antenna, space satellite, space station or space base) sent to
the Earth orbit are limited by possibility of a launch vehicle. The large-size construction can be created by the use of the technology
of the polymerization of fibers-filled composites and a reactionable matrix
applied in free space or on the other space body when the space construction
will be working during a long period of time. For example, the fabric
impregnated with a long-life matrix (prepreg) is prepared in terrestrial
conditions and, after folding, can be shipped in a container to orbit and kept
folded on board the station. In due time the prepreg is carried out into free
space and unfolded by inflating. Then a reaction of matrix polymerization
initiates. After that, the artificial frame can be fitted out with the
apparatus or used for any applications.

In this case, there is no limitation for size
and form of the space construction, there is no necessity for some launch vehicles for
the creation of high-size space construction.

However, conditions of free space
have a destructive influence on polymer materials and especially for uncured
polymer matrix of composite. In the free space the material is treated by high
vacuum, sharp temperature changes, plasma of free space formed by space rays,
sun irradiation and atomic oxygen (on low Earth orbit), micrometeorite fluency,
electric charging and microgravitation. Our preliminary studies of
polymerization process in high vacuum, space plasma and temperature variations
showed that the polymerization process is available in free space under space
factors and the composite cured in simulated free space environment has
satisfied mechanical properties.

The present project includes:

- Investigation of the polymerization process and
structure of selected composite material in simulated space environment;

This blog has been done to tell a story how can we go to space forever, to find an university where these study will be placed, a company where the developed technology can be realised and an investor who is ready to contribute into new era of space business.